1. Field of the Invention
The present invention relates to a method and a system for positioning a glass plate, and a method and a system for bending a glass plate.
2. Description of the Related Art
Explanation will be made about a conventional production procedure for a curved glass plate, which is used as automobile windows. First, a flat glass plate, which has been cut in a certain shape, is conveyed through a heating furnace by a roller conveyor to be heated to a glass bending temperature (600 to 700° C.) by a heater in the heating furnace. Next, the heated glass plate is conveyed onto a bending stage to be pressed, be bent by its own weight or be subjected to another bending treatment so as to have a desired curvature there. After that, the bent plate glass is conveyed onto an air cooling/tempering stage, and cooling air is blown against both surfaces of the bent plate glass from upper and lower blowing heads provided in the air cooling/tempering stage to cool and temper the plate glass, producing a tempered glass plate having a desired curved shape.
The glass plate, which has been conveyed to an outlet of the heating furnace, is positioned so as to have its posture conformed to a reference posture by a positioner and then is conveyed onto the bending stage to be bent (see U.S. Pat. No. 5,669,953). The positioner comprises a plurality of arms for contact with a front edge and lateral edges of a glass plate, and a dive unit for moving these arms to position the glass plate so as to take the reference posture. The length and the shape of the arms need to correspond to the size and the shape of the glass plate. Whenever the model type of a glass plate (the model type of a product) to be produced changes (hereinbelow, referred to as the job change), it is inevitably necessary to use a positioner suited to the changed model type.
The applicants have proposed a glass plate bending system using a roller conveyor, which is novel and innovative (see U.S. Pat. No. 6,397,634). This system includes a roller conveyor comprising a plurality rollers provided so as to be independently and vertically movable. The system lowers rollers lying just under a glass plate in synchronization with conveyance of the glass plate to form the glass plate in a desired curved shape upon completion of conveyance. This bending system needs no exchange of parts irrespectively of the model type of a glass plate to be bent. This bending system can substantially eliminate the job change on the bending stage since the system can bend a glass plate so as to have a desired curvature only by controlling the vertical moving amount of the bending roller, the conveyance speed of the glass plate or the like.
The conventional positioner has caused several problems since, in order to bend a glass plate with good precision, the glass plate needs to be accurately positioned so as to take the reference posture before being conveyed onto the bending stage. Specifically, it has been necessary to use a positioner suited to the model type of a glass plate to be bent as stated earlier. In order to position a glass plate, the arms of the positioner needs to come into contact with the glass plate, which has been heated to the glass bending temperature and been softened. As a result, there have been caused problems that the glass plate is deformed by the impact caused by the contact with the arms, and that the glass plate is abraded by slippage on a roller. Additionally, there has been caused a problem that there is a limitation to the improvement in productivity since it is necessary to stop the glass plate in the middle of conveyance before positioning the glass plate.